This invention relates to a controller for a motor/generator which drives a plurality of rotors with a single stator coil.
Tokkai Hei 11-275826 published by the Japanese Patent Office in 1999 discloses a synchronous motor/generator which drives a plurality of rotors independently by applying composite polyphase alternating currents to stator coils.
The invention disclosed in Tokkai Hei 11-275826 is a part of U.S. Pat. No. 6,049,152 that was issued in the United States after the priority date of this patent application.
In this motor/generator, the alternating currents supplied to the coils are generated by providing inverters for each phase of the coils and by supplying a pulse width modulation signal (hereafter referred to as PWM signal) to the base of a transistor constituting each inverter.
Since electrical power supplied to each coil is equal in this motor/generator, a duty ratio of the PWM signal is low when a load on the motor/generator is low. That is to say, the pulse width is narrowed. As a result, the current applied to the coil comprises numerous high frequency components during low load.
However high frequency components increase core loss in the motor/generator and the conversion efficiency from electrical energy to mechanical energy is reduced.
Further, in this motor/generator, when a part of the inverter is malfunctioning, torque generated by the rotor is reduced and sometimes the rotor is caused to stop.
It is therefore an object of this invention to improve energy conversion efficiency during low load running in a motor/generator.
It is a further object of this invention to prevent reductions in torque generated in the rotor resulting from malfunctioning of the inverter.
In order to achieve the above objects, this invention provides a controller for a motor/generator that has a plurality of groups of coils and is operated by supplying a polyphase alternating current to each of the plurality of groups of coils. The controller comprises a plurality of inverters each of which converts a direct current into the polyphase alternating current and supples the polyphase alternating current to each of the plurality of groups of coils in response to an input signal. The controller further comprises a sensor which detects a load of the motor/generator, and a microprocessor programmed to compare the load with a reference load, and control the input signal to a specific inverter to stop supplying the polyphase alternating current when the load is smaller than the reference load.
This invention also provides a method for controlling a plurality of inverters which drive a motor/generator. The motor/generator comprises a group of coils. Each of the inverters converts a direct current into a polyphase alternating current and supplies the polyphase alternating current to each of the plurality of groups of coils in response to an input signal. The control method comprises detecting a load of the motor/generator, comparing the load with a reference load, and controlling the input signal to a specific inverter to stop supplying the polyphase alternating current when the load is smaller than the reference load.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.